FIGS. 1 and 2 are views showing a structure of a conventional typical balanced vane-type rotary machine. As shown in FIGS. 1 and 2, a balanced vane-type rotary machine 100 comprises a rotor 102 housed in a cam casing 101, vanes 103 inserted in the rotor 102 and having distal ends held in contact with an inner circumferential surface of the cam casing 101, a front cover 104 and an end cover 105 surrounding both sides of the rotor 102 and the vanes 103 inserted in the rotor 102, and a main shaft 109 coupled to the rotor 102 and rotatably supported by bearings 106, 107 mounted in the front cover 104 and the end cover 105. The cam casing 101 of the balanced vane-type rotary machine 100 has first ports (discharge ports if the balanced vane-type rotary machine 100 is a pump, supply ports if the balanced vane-type rotary machine 100 is a motor) 110, 110 and second ports (suction ports if the balanced vane-type rotary machine 100 is a pump, return ports if the balanced vane-type rotary machine 100 is a motor) 111, 111, the first ports 110, 110 and the second ports 111, 111 being located at two locations symmetrical with respect to the main shaft 109 of the rotor 102. Reference numeral 114 represents vane slits.
If the balanced vane-type rotary machine 100 is a pump, then when the rotor 102 is rotated as indicated by the broken-line arrow A2, a working fluid drawn from a suction opening 112 as indicated by the broken-line arrow A1 flows from the second ports 111, 111 into the rotor 102. Then, a pumping action of suction and discharge of the working fluid is carried out twice while the rotor 102 is making one revolution, and then the working fluid is discharged through the first ports 110 from a discharge opening 113 as indicated by the broken-line arrow A3.
If the balanced vane-type rotary machine 100 is a motor, then a working fluid supplied from a supply opening (discharge opening of the pump) 113 as indicated by the solid-line arrow B1 flows from the two first ports 110, 110 into the rotor 102, and the pressure of the introduced working fluid acts on the vanes 103 projecting from the rotor 102 to produce a torque, thereby rotating the rotor 102 as indicated by the solid-line arrow B2. Thereafter, the working fluid is discharged through the second ports 111, 111 from a return opening (suction opening of the pump) 112 as indicated by the solid-line arrow B3.
In both of a pump or a motor, because the balanced vane-type rotary machine 100 is provided with the two first ports (discharge ports if the balanced vane-type rotary machine 100 is a pump, supply ports if the balanced vane-type rotary machine 100 is a motor) 110, 110 and the two second ports (suction ports if the balanced vane-type rotary machine 100 is a pump, return ports if the balanced vane-type rotary machine 100 is a motor) 111, 111, symmetrically with respect to the main shaft 109, the pressure around the rotor 102 is in equilibrium, and the shaft loads, caused by the fluid pressure, in the radial direction of the main shaft 109 are balanced, thus reducing bearing loads.
If the balanced vane-type rotary machine 100 is a pump, then the first ports 110, 110 serve as fluid discharge ports, and the second ports 111, 111 serve as fluid suction ports. When the main shaft 109 rotates (the rotor 102 rotates), the suction opening 112 draws the fluid, and the discharge opening 113 discharges the fluid. If the balanced vane-type rotary machine 100 is a motor, then the first ports 110, 110 serve as fluid supply ports, and the second ports 111, 111 serve as fluid return ports. The pressurized fluid from the supply opening (discharge opening of the pump) 113 produces a driving force to rotate the rotor, and the fluid returns through the return opening (suction opening of the pump) 112 to a tank. Next, problems of the vane motor having the above conventional structure will be described below:
[Problem 1]
In the vane-type rotary machine (used as a motor) having the structure shown in FIGS. 1 and 2, as shown in FIG. 3, two branch flow passages 122, 123 branched at a branch point 124 of the supply opening (supply port) (discharge opening of the pump) 113 and communicating with two vane chambers 120, 121, and two branch flow passages 132, 133 extending from two vane chambers 130, 131 to the return opening (return port) (suction opening of the pump) are arranged as follows: The length L122 of the branch flow passage 122 (the supply opening 113→the branch point 124→the branch flow passage 122→the vane chamber 120), and the length L123 of the branch flow passage 123 (the supply opening 113→the branch point 124→the branch flow passage 123→the vane chamber 121) have a relationship of L122≠L123. The length L132 of the branch flow passage 132 (the return opening 112→a branch point 134→the branch flow passage 132→the vane chamber 130) and the length L133 of the branch flow passage 133 (the return opening 112→the branch point 134→the branch flow passage 133→the vane chamber 131) have a relationship of L132≠L133.
For downsizing the vane-type rotary machine (a pump, a motor), the diameters of the respective branch flow passages need to be reduced. If the diameters of the respective flow passages are reduced in the conventional vane-type rotary machine having the branch flow passage arrangement of the above relationship (L122≠L123, L132≠L133), then since the distances of the branch flow passages to the vane chambers are different from each other, in the example shown in FIG. 3, most of the fluid supplied under pressure flows into the branch flow passage 122 from the supply opening 113 to the vane chamber 120 and having a short distance. However, because the branch flow passage 123 from the supply opening 113 to the vane chamber 121 is longer than the branch flow passage 122, the fluid supplied under pressure flows in a small amount into the branch flow passage 123 having a large pressure loss. The vane-type rotary machine 100 having the above conventional structure is expected to cause the following problems when it is downsized:
(1) The pressure around the rotor 102 is not held in equilibrium and radial loads acting on the main shaft 109 are nonuniform, thus posing large loads on the bearings 106, 107, and lowering the mechanical efficiency due to an increase in the friction of the bearings 106, 107 and decreasing the service life of the bearings.
(2) Since the working fluid acting on the vanes 103 is supplied substantially only from one pressure liquid chamber (the vane chamber 120 under the higher pressure), the output torque becomes small, and the mechanical efficiency is lowered.
Regarding the above, in the case where the vane motor is replaced with a vane pump (the supply flow passage system of the motor becomes the discharge flow passage system of the pump), the following problems arise for the above reasons:
(3) Since different pressures act on the pump discharge branch flow passage system (the vane chamber 120 and the vane chamber 121), the pressure around the rotor 102 is not held in equilibrium and the shaft loads in the radial direction acting on the main shaft 109 are nonuniform, resulting in an increase in the load on the bearings acting on the main shaft 109.
Inasmuch as the relationship of the suction flow passage system, i.e., the relationship of the length L132 of the branch flow passage 132 and the length L133 of the branch flow passage 133 is given as L132≠L133, the following problem arises:
(4) When the fluid is drawn in, the fluid is introduced into the vane chamber 130 near the suction port. Because the vane chamber 131 spaced from the suction port is greatly affected by the suction resistance (back pressure), the fluid is introduced in a small quantity, resulting in a reduction in the pump suction performance and a reduction in the volumetric efficiency.
[Problem 2]
The problems (1) through (4) in the [Problem 1] may arise even if the branch flow passages are arranged with a relationship of L122=L123, L132=L133 (L122 represents the length of the branch flow passage 122, L123 represents the length of the branch flow passage 123, L132 represents the length of the branch flow passage 132, and L133 represents the length of the branch flow passage). Specifically, even if the lengths of the flow passages are the same, the above problems occur because different pressure losses are caused from the branch points to the vane chambers due to different diameters of the flow passages, the different numbers of bends, and the like.
Additionally, in the case where the vane-type rotary machine is downsized, the diameters and distances of the branch flow passages cannot necessarily be equalized due to dimensional limitations. The above problems can be avoided by taking measures to make the lengths and diameters of the branch flow passages identical, but those measures pose a limitation on downsizing of the vane-type rotary machine which is a major target to be achieved.
[Problem 3]
As shown in FIG. 4, the cam casing 101 of the vane-type rotary machine 100 has an inner surface configuration which is defined by large arcs 140, small arcs 141, and smooth curves interconnecting those arcs. The angular ranges of the large arcs 140 and the small arcs 141 have to be appropriately calculated and designed in order to obtain predetermined performance of the vane-type rotary machine, thereby forming the cam casing 101.
With the structure of the conventional balanced vane-type rotary machine 100, as shown in FIG. 4, the angular ranges of the large arcs 140 and the small arcs 141 have been established by forming cocoon-shaped or arcuate-recess-shaped ports 142 in the cam casing 101, or in the end cover 105 as shown in FIG. 5. For downsizing the vane-type rotary machine 100 having the conventional structure, however, the cocoon-shaped or arcuate-recess-shaped ports 142 which require special shapes and manufacturing accuracy need to be directly formed in the small-sized cam casing 101, and hence such formation is difficult and expensive. Conversely, the structure is complicated, and hence it is difficult to downsize the vane-type rotary machine.